1. Field of the Invention
The present invention relates to a deposit discharge system and a method of discharging deposit from a water storing place, e.g., dam.
2. Description of Background Art
In a water storing places such as a dam, functions of the dam are lost when pondage of the dam is, reduced. To maintain the functions, deposits in water, e.g., sands and stones, are dredged so as to maintain enough water level. Stones included in the deposits dredged are used as aggregates of concrete, and others are used for reclamation, etc.
However, if the dam is dredged, no stones and sands are conveyed downstream. Therefore, the natural balance is lost and new environmental problems are occurred. For example, organic components made in mountains stored by the dam; no nourishment or foods of plankton are supplied to the sea, so that number of fish is reduced. Further, no stones and sands are conveyed downstream, so that a riverbed is extremely washed out and sandy beaches are disappeared.
In a huge dam, water flows little and stays there for a long time. Unlike a small dam, stones and sands are apt to precipitate and deposit therein. Almost all fine grains in water are also deposited. For example, about 10,000,000 m3 of fine grains have been deposited for 40 years. It is very difficult for a dredging boat to remove a huge amount of stones and sands, so it is also difficult to maintain effective pondage of dams.
As shown in FIG. S, a system for discharging deposits 22 from a huge dam 60 was proposed. The system directly flows flood flow and solid-liquid two-phase flow from the upstream side of the dam to the downstream side 64 via a bypass tunnel 30. A plurality of supplementary tunnels 32, which communicate a water storing place 20 to the bypass tunnel 30, are formed in a coast 23 of the dam. With this structure, deposits can be discharged from a plurality of positions in the water storing place 20.
Deposit discharging ports 62 of the supplementary tunnels 32 are opened in a bank of the dam so as to safely flow the deposits 22. Water gates for opening and closing the discharging ports 62 and a mechanism for securely actuating the water gates are required. If the discharging ports 62 are not securely closed, water stored on the upstream side of the supplementary tunnels 32 will be leaked out therefrom.
However, it is difficult to securely open and close the water gates when a large amount of water including deposits flows. Even if the water gates are opened and closed, the open-close mechanism must be large. To discharge stones and sands deposited thicker than prescribed thickness, height of the water gates must be equal to or higher than the thickness of the deposits. The water gates must bear up against high water pressure, so that they must have large structures.
The deposits 22 must be uniformly removed from a large area of the water bottom so as to maintain proper pondage.
However, in the case of discharging the deposits to the bypass tunnel 30 via the water gates and the supplementary tunnels 32, the deposits near the water gates can be effectively discharged, but other deposits cannot be discharged effectively. Therefore, the deposits 22 distributed in the large area cannot be fully removed.
To solve this problem, a siphonal discharge system shown in FIG. 12 was proposed.
A discharge tube 70 has a suction port 71 opened so as to face the water bottom face 29 of the water storing place 20 and a discharge port 78 opened in a water path 80 located on the downstream side. A tube part 73 of the discharge tube 70, which is located on the suction port side, is supported by a boat 82; a mid part 76 is bent and routed above the water level 21 so as to get over the dam banking 25.
The discharge tube 70 is filled with water by a high power pump 84 installed in the water, so that the siphonage can be occurred. When the siphonal action is stopped, an air valve 77, which is provided to a top of the mid part 76, which is bent, of the discharge tube 70, is opened so as to introduce air into the discharge tube 70.
A straight tube part 72, which is close to the suction port 71 of the discharge tube 70, is vertically arranged. The straight tube part 72 can be extended and contracted according to a distance between the water surface 21 to the water bottom 29. For example, it is formed by an inner tube and an outer tube, which can be vertically extended and retracted with respect to the inner tube.
The discharge tube 70 has a bendable section 74. The suction port 71 of the discharge tube 70 can be turned, in a horizontal plane, about the bendable section 74. To horizontally turn the suction port 71, the boat supporting the part of the tube on the suction port 71 side is moved. By moving the boat, the suction port 71 can be moved along a circular track. A float 75 makes the discharge tube 70 stay on the water surface.
In the above described conventional system, the discharge tube 70 is installed to get over the dam banking 25. With this structure, the discharge by siphonal action is limited. If speed of solid-liquid two-phase flow is equal to or lower than prescribed speed, solids begin to precipitate. For example, if volume percentage of solids is 1%, the speed is about 2.5 mlsec. At this speed, deposits close the tube. To solve this problem, the conventional system employs the high power source, e.g., the pump 84, so as to add jet flow. Namely, the high power source maintains a filled water channel in the discharge tube 70. Note that, the word xe2x80x9cfilled water channelxe2x80x9d means a channel filled with water and having no free water surface.
The conventional deposit discharge system must have the high power source, e.g., the pump 84. Therefore, the structure must be complex, and the siphonal structure is not essential. With this complex structure, initial cost and running cost of the discharge system must be increased.
Since the discharge tube 70 gets over the dam banking, the mid part of the discharge tube 70 must be bent upward. The discharge tube 70 must be bent at three points at least, so that friction loss in the tube must be greater. Deposits, which must be passed through the discharge tube 70, are deposited in and closes the tube.
Further, the discharge tube 70 cannot be made longer due to the friction loss therein.
An object of the present invention is to provide a deposit discharge system having a simple structure and capable of easily and efficiently discharging deposits.
Another object of the present invention is to provide a deposit discharge system in which no deposits close the tube and which is capable of efficiently discharging deposits.
Further, another object of the present invention is to provide a method of efficiently discharging deposits with the deposit discharging system.
To achieve the objects, the present invention has following structure.
The deposit discharge system comprises: a discharge tube having a suction port opened so as to face a water bottom face of a water storing place on which deposits are deposited, a straight tube part vertically extending upward from the suction port, and a discharge port opened in a water path on the downstream side of the water storing place for draining the deposits from the water storing place to the water path together with water stream, characterized in: that the discharge tube is pierced through a bank hole, which is located below the water level of the water storing place, and suspended by a boat, which floats on the water, so as to locate the discharge tube under the water level of the water storing place; and that the discharge tube is vertically moved by an elevating unit, which is provided to the boat, so as to move the suction port close to and away from the water bottom face of the water storing place with prescribed cycle, whereby pulsating flow and plug flow, in which high solid-concentrated part and low solid-concentrated part are alternately appeared, are generated.
In the deposit discharging system of the present invention, the pulsating flow and the plug flow can be actively generated in the vertical tube part by vertically moving the vertical tube part; further a centripetal motion of turbulent flow in the vertical tube part can be accelerated, so that the deposits deposited in the water storing place can be efficiently discharged, as the solid-liquid two-phase flow, and without friction loss, which is caused by colliding solids with an inner face of the tube. In the deposit discharge system, the boat may suspend and locate the discharge tube under a hydraulic gradient line.
In the deposit discharge system, an air valve, which is capable of introducing air to and discharging air from the discharge tube, may be provided to the discharge tube so as to generate and stop siphonage caused by waterhead difference. With this structure, generating and stopping the siphonage can be easily and properly controlled.
In the deposit discharge system, the elevating unit may have means for adjusting the cycle of the vertical movement of the suction port. With this structure, generation of the pulsating flow and the plug flow and volume concentration of solids in the solid-liquid two-phase flow can be easily adjusted, so closing the tube can be prevented by the simple structure and simple operation, further the solid-liquid two-phase flow can be efficiently discharged.
The deposit discharge system may further comprise: an arm member having one end, which is pivotably connected to an end of the straight tube part near the suction port, and the other end, which is capable of turning upward and downward; a fulcrum member pivotably connected to a mid part of the arm member and capable of pivoting with respect to the arm member with maintaining a vertical posture in the vertical direction in the water; and a chisel pivotably connected to the one end of the arm member and capable of maintaining a vertical posture in the water, the chisel agitating the deposits on the water bottom face, wherein power transmitting member, e.g., a wire, of the elevating unit is connected to the chisel. With this structure, the chisel agitates the deposits, so that the deposits can be further efficiently discharged.
In the deposit discharge system, a mid part of the discharge tube other than the vertical tube part may be capable of bending in a horizontal plane. With this structure, the deposits in a broad area can be discharged.
In the deposit discharge system, a straight part of the discharged tube may be pierced through the bank hole formed in a dam banking and capable of moving, in the bank hole, in the longitudinal direction thereof, and a plurality of roller-shaped supporting members, which assist smooth movement of the discharge tube, may be provided near the bank hole. With this structure, the deposits in a broad area can be discharged without reducing the discharging efficiency.
In the deposit discharge system, a space between the bank hole and the discharge tube may be water-tightly sealed by a sealing member, which is formed like an air bag and capable of pressing when air is introduced therein. With this structure, the discharge tube can be moved and the space can be easily and securely sealed.
The method of the present invention is executed in a deposit discharge system including: a discharge tube having a suction port opened so as to face a water bottom face of a water storing place on which deposits are deposited, a straight tube part vertically extending upward from the suction port, and a discharge port opened in a water path on the downstream side of the water storing place for draining the deposits from the water storing place to the water path together with water stream, the method comprises the steps of: piercing the discharge tube through a bank hole, which is located below the water level of the water storing place; suspending the discharge tube by a boat, which floats on the water, so as to locate the discharge tube under the water level of the water storing place; and vertically moving the discharge tube by an elevating unit, which is provided to the boat, so as to move the suction port close to and away from the water bottom face of the water storing place with prescribed cycle, whereby pulsating flow and plug flow, in which high solid-concentrated part and low solid-concentrated part are alternately appeared, are generated.
In the method, the down movement of the suction port is free fall so as to effectively get effects of the pulsating flow, the plug flow, and the ground effect, which is occurred when an open end of a tube is rapidly moved close to a bottom face and which is capable of concentrically generating swirl and rising flow in the tube. By this method, the deposits can be efficiently discharged. By vertically moving the suction port, effects caused by the plug flow and the- pulsating flow, which are occurred by the vertical movement, and ground effect can be employed. Experimental results are shown in FIG. 11. Namely, the discharging efficiency of the method was 4.8 times as much as that of a conventional method.
Further, in the method, the elevating unit of the boat may suspend the discharge tube in a state, in which a part of the discharge tube on the suction port side other than the vertical tube part is located above the bank hole and the part of the discharge tube is located at the highest position thereof, whereby the discharge tube can be inclined with down gradient so as not stay deposits in the tube. With this method, the discharge tube can be properly arranged under the hydraulic gradient line, so that the deposits can be efficiently discharged without closing the tube.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples; while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.